6U8 6GH8 ECF82 to 7199 Vacuum Tube Adapter Socket Converter Pre Amplifier Part
Top is 6U8,6GH8,ECF82. If want to try 6U8,6GH8,ECF82. Only plug it into the adapter. Bottom is 7199. Amplifier design use 7199. Trying different voice by tube with adapter. Needn't change amplifier anything.